Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
I talked to two people in the high end audio field that don't believe in the ultrasonic hype in high end audio. I was told that that those so called add on supertweeter, tweeters that extend past 20-25 hertz and those in loudspeakers are really not giving you "more information, i.e. ultrasonics on recording". Most mikes rarely go past 20 on the top end and some ribbon types not past 25. Interesting some very high speakers don't go past 22.5 on the top end are are very expensive and highly revered such as, Wilson, Rockport Technologies, Martin Logan, etc. Makes sense, if most mikes, 99% don't capture info / ultrasonics, than what is the use? In theory it sounds great but in practice it just does not pan out. What about those direct to disc lps, recorded directly to the lath, no tape, probably still limited by the mikes. Crazy. What do you guys think. Makes sense huh.Ger
And if it sounds like crap at 30,000hz, then they can write a letter to stereophile, or go online and ask how to get this big stupid human to fix things..
Very Buddhist of you!!
"In this land right now, some are insane and they're in charge. To hell with poverty, we'll get drunk on cheap wine."
There is a valid school of thought that when one extends the bandwidth of a component to beyond useful frequencies, that the audible range has the potential to be more linear. Kind of like having a car that "can" go 200 mph, and therefore is quite comfortable at 80. Or, like having a subwoofer that "can" deliver 10 Hz, and is quite comfortable at 30. Or like having a midrange driver than is good to 5000 Hz, but you cross it at 2500.
There's also the issue of "beat frequencies" - audible frequencies generated by the interaction of very high frequencies, particularly when music is performed by multiple players indoors. However, since those beat frequencies are already in the audible spectrum, there's no need to record the ultra-high frequencies which generated them.
In any case, unless one possesses a system where every component is capable of reproducing ultra-high audio frequencies AND has source material which includes it (meaning that the recording was made with similar HF capabilities, and that the playback media has captured it), the question is moot. (I've always wanted to use that word.)
Ultrasonic signal behave nonlinearly in air? that's right, two ultrasonic tones - say 100KHz and 101KHz produce an audible tone at 1KHz!
Air induced distortion - it is also dependent on level or the signals. That's right - you can produce a heterodyne loudspeaker that produces audio frequency sound "over there" but not here by using two ultrasonic loudspeakers.
Three most important things in Audio reproduction: Keep the noise levels low, the power high and the room diffuse.
"Ultrasonic signal behave nonlinearly in air? that's right, two ultrasonic tones - say 100KHz and 101KHz produce an audible tone at 1KHz!
Air induced distortion - it is also dependent on level or the signals."
You're confusing two different things.
Yes, air is nonlinear - progressively distorting more and more as the SPL is raised.
But, your example is about "beat frequencies" - the periodic alignment/non-alignment of the pressure of two different tones. This can easily be demonstrated by simply singing a tone which is slightly different than the tone on a record, or by listening to the result of two musicians playing the same tone but slightly out of tune with each other.
If one were to produce a signal at say 30KHz and another at say 30.1KHz, there IS a 100hz beat (amplitude modulation ) effect BUT only when there is non-linearity, does the 100Hz become audible.
Non-linearity produces a sum and difference frequency when two signals add, a beat frequency is the rate of amplitude modulation of two periodically adding and canceling signals such as one note played on two nearly in tune guitar strings.
Air in not the only thing that can be non-linear too, ultrasonic energy within an audio system can cause other audible effects when the system has significant non-linearity.
Amplifiers for example normally have a small series choke at the output with the intention of DE-coupling the output stage from the speaker wire which can act like an antenna or parasitic capacitance.
Fwiw, if i am not mistaken, the big guy is a hifi buff who happens to also be a rep for a VERY highly respected (as in world wide) line of acoustic and vibration measurement equipment.
The term "non-linear", as used here, refers to a component (such as air) in the chain reproducing the input signal as a disproportionately distorted signal as the input signal varies. For example, air more or less reproduces sound normally at typical day-to-day sound levels, but has disproportionally increasing distortion as the sound level increases.
This is one reason why most horns have "issues". The SPL in the throat can be extremely high.
Air follows the “gas law” which means it with a large change in pressure, it is not a linear “spring”.
In the case of what we call airborne sound we reach 194dB when the negative pressure =0 and the positive 2X ambient pressure. It is possible to have a greater positive pressure however but then it’s called a shock wave. In a normal sine wave, the non-linearity can be seen once the intensity is in the high 150’s or above (dB). Because the positive pressure is slightly warmer, it travels faster and over many wavelengths, the sine wave processes into a saw tooth wave.
In audio, one has horn throat distortion which is related to the high frequency sound intensity and how slowly the horn area expands (the more slowly, the worse it is).
"In audio, one has horn throat distortion which is related to the high frequency sound intensity"
Horn throat distortion, because of the high SPLs up in there, affects ALL frequencies produced by the horn.
Actually it is the same effect as the "shocking up" (progression of a high intensity sine wave into a saw tooth wave), if sound were traveling though a pipe, then it is the intensity and number of wavelengths that govern this, the greater either is the greater the issue.
In a horn, the pressure falls with increasing area and so one finds for a given initial throat intensity, the problem is worse with increasing frequency and decreasing expansion rate. At the low frequency end of most horns response the driver linearity is by far dominant issue.
Hey Tom, thanks for the clarification/correction. I was over-generalizing my point.
As an aside... My long lost friend John Meyer, back in the early 70s, hit on the idea of using electronics to "pre-distort" the signal in basically the opposite manner that the horn distorts it, effectively cancelling a large percentage of the distortion and reducing it by a significant amount, resulting in a much cleaner sound quality. I thought that was pretty novel.
Repeated tests have shown that subjects are aware of ultrasonic content even if they can't hear it in the traditional sense. Ultrasonic content still excites the hearing mechanism, which in turn signals the brain that something is there.
In the tests (US Army in the early 50's and CalTech in the mid 90's), subjects heard sounds both with and without ultrasonic content. When said content was removed from the sound, subjects identified that something had changed but could not specifically pinpoint what had changed. The important point is that they were aware of the lack of ultrasonic content, even if they did not know in the traditional sense that the ultrasonic content was missing.
My theory is that the brain recognizes ultrasonics on a subconscious level, which in turn influences how consciously perceive the sound that we "hear" and process normally.
(refer to link)
Is it real or nonsense, I don't know. But supposedly the Japanese-language TrueHD soundtrack on the "Akira" Blu Ray contains program content beyond 90 kHz! I don't have speakers capable of reproducing that kind of frequency.
I wish the writers of that website would get their data straight. DVD standard is capable of 96K/24 (48kHz audio) and DVD-Audio capable of 192k/24 (96khz audio) BD is not exclusive to 192K/24. DVD-Wav also can go as high as the limits of PCM (384k/24) as well as DXD (352.8k/24) and hard drives and SSD as well as all memory chips can store the content for playback. The cd specifications are correct on the site.
There are recordings that have musical energy well above 30 kHz. I have a few dozen such digital downloads, mostly 192/24, such as the Acousence recordings that can be downloaded from Linn Records. Even older analog sourced recordings (at 192/24 or 96/24) have high frequencies up to about 30 kHz, as limited mostly by tape. Many of these can be downloaded from HDtracks. The spectrum plot feature in iZotope RX makes this obvious. There are commercial microphones being used to record classical music that advertise response to 100 kHz.
There are speakers that go up to 40 kHz. (I have such a pair.)
Whether response from 20 to 40 kHz affects sound quality is a separate issue. It's certainly inaudible on sine waves. (Fifty years ago I could hear 21 kHz, but now it's only 14 kHz at moderately loud volume levels.)
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Roll offs above the audio band will cause phase shifts within the audio band that are easily measurable. Response two octaves above the audio range can, in some circumstances, minimize this.
Now is the way to go about this letting the existing tweeter roll off causing phase shifts and then adding yet another tweeter and crossover to compensate? I'm not sure.
But then again, some tweeters roll off in the audible band, the Electo-Voice T35 tweeters in my Cornwalls hit the wall at a measured 12K and take the elevator down from there. My apature ribbons, crossed over at 12K add a bit more air to the top end. That said, I ususually don't hassle with them, but that may have more to do with the measured peak in the T35 making it hard to mate with the super tweeters.
A number of things in hifi now depend on ones belief they work to work.
That sounds tacky I know but what you know has a very strong impact on how you interpret things. G
oogle the Mcgurke effect to see an example of what you actually hear taking a back seat to what you see and know.
One can hear ultrasonic energy too if it’s loud enough, I used to work on ultrasonic transducers made for acoustic levitation and used in a couple experiments flown n the space shuttle (STS-7 and STS-51a). Experiments have shown that under the right conditions, one can detect very short time difference between ears corresponding to the 100-200KHz range.
THIS is not the same as hearing / detecting a tone at those frequencies though and what people describe as “air” is more likely to be in the 8-10KHz range.
When a purveyor of a “super tweeter” and other magic stuff posted about them in one of the forums here, after some pressing, he was eventually able to admit they do not actually produce sound, they are not actually driven by the amplifier signal and that even though they appear to be very small horns, are pitched as a super tweeter and hooked up like speakers.
AS you mentioned it is very hard to capture very high frequencies also and a medium like a CD cannot store signals above 22KHz and are brick wall filtered to keep them out. That’s actually ok too as most people over vastly estimate the frequency when presented with a tone, adults generally can’t hear even 20KHz unless it’s loud and against a silent background. Google the ears response curves to see this part of the problem, google “equal loudness curves” which show the difference between actual measured loudness and how loud it sounds to ones ears.
Danley Sound Labs
The only valid point in your whole post is brick-walled CD - and that concern goes away, if one deals with hi-rez files via computer playback.
I'm pretty sure you know that modern DACs, amps etc. are very comfortable way above 50 KHz. Mechanisms by which ultrasonics affect human brain are not limited to HEARING, but even if they were - there's more than one research showing that some people are capable of hearing above 24 KHz.
Science is not limited to only the part of it that you're comfortable with, you know.
“The only valid point in your whole post is brick-walled CD - and that concern goes away, if one deals with hi-rez files via computer playback.”
If you mean capturing and reproducing sounds that exist in music or environmental sound, then you profoundly under estimate how hard it is to both capture and reproduce those sounds and that in the presence of other sound lower in pitch are easily masked masked.
For example, what loudspeaker transducer do you know of that can cover 50KHz or higher and what sensitivity is it relative to the speakers below? What microphone has both a low enough noise floor for hifi and response that high?
I record in the 24/96 format because of the noise floor and uncompressed recordings but what one can say is that if anything comes out of a CD player above about 22KHz, it not part of the recorded signal.
Also, I didn’t say you can’t hear above 20KHz, I said it had to be loud enough to be audible, just like low frequency sound (see link).
"What microphone has both a low enough noise floor for hifi and response that high?"
Earthworks claims that some of their models have a bandwidth up to 50KHz.
Just an idle thought - I'm not saying it's useful.
Regarding the "tiny" B&K mic... are you talking about the 1/8" model? Yeppers, those puppies be 'spensive. They're also not very good for "normal" audio recording. The low end and output level are issues when mated to "normal" audio gear. Although, the Grateful Dead did use the 1/4" (I think 4135?) successfully as a differential mic setup for vocals, but, yes, the cost was exhorbitant. ('Course, as part of the "one percent", they had the money. ;) )
Yes, among others, I have a pair of M55's which are -3dB at about 48KHz and a 1/8 inch B&K which is good to about 80KHz. I am very familiar with the difficulties involved at the producing end as well.
It is the noise floor which becomes a problem when you have a small enough mic to go that high.
The solution i have been working on allows a smaller mic but also lowers the noise floor.
Personally i believe a large part of the problem is at the capture end and it isn't so much one of lack of extension.
See if the Train or Harley at the bottom of the linked page doesn't have an unusually "real" impression, try them with headphones first.
"The solution i have been working on allows a smaller mic but also lowers the noise floor."
I'm pretty sure that that's what all the major and minor mic manufacturers are doing.
Higher output, smaller diaphragm, lower noise. Huh, who'd a thunk it.
“I'm pretty sure that that's what all the major and minor mic manufacturers are doing.”
Yes but just like the 400 mile per gallon carburetor, the laws of physics can be a real pain in the rear when in the way.
“Higher output, smaller diaphragm, lower noise. Huh, who'd a thunk it.”
Maybe someday they will make a leap forward in that but for now, like all of us, they are limited by physics and real world materials to what we have now.
My approach doesn’t defeat physics, it uses the laws a little differently.
If you are interested in audio / recording technology enough to listen to something, try the Harley or Train recordings at the bottom of the page with headphones and make a judgment on the stereo image and noise floor based on sound.
Herding those air molecules surrounding the microphone is more difficult than herding cats. :-)
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
A medical research group I've worked with adds digitally generated infra and ultra sound to music while a person in a catatonic state is placed in a MRI to scan brain activity. When exposed to the infra and ultra sound there brains light up. Showing that there are registering it. Some have even improved a bit from such treatments. As far as use in music I have built super tweeters for some but there mostly used on loudspeakers that have rolled off response to begin with thus owners complained sound quality as lacking in air or detail.
I know also that one can synchronize and change ones state of consciousness using beat frequencies presented to each ear (entrainment I think they called it), in the 90’s they sold these “light and sound” machines for meditation and such. Also, we supplied a number of VLF transducers for preventing bowel adhesion's after surgery and for some kind of music therapy bed.
There is the nagging difficulty with ultrasonic energy within music though.
In the late 90’s I made a living as a for hire transducer designer and one job was for a professor at Northwestern U in Evanston il. He was researching the heterodyne loudspeaker which used ultrasonic energy and the air’s non-linearity to project sound. I built a focusing electrostatic speaker (the levitation transducers didn’t have enough bandwidth). At the point it was starting to hiss and crackle from high Voltage, that could produce about 160 dB at 55KHz at the focal point at 36 inches. To measure that high in frequency and SPL, required a TINY B&K microphone ($ huge $) who’s noise floor would be prohibitive for recording.
When you modulate the 55Khz carrier frequency and or amplitude, the non-linearity in the air produces an audible sound.
This same idea resurfaced several times since, one under his student Joe.
The problem is the fidelity is at best a tinny transistor radio and while the carrier was not audible per say, about half the test subjects complained about a headache after exposure suggesting the 55Khz was doing something.
The point is, when you have the stuff to measure up that high, you really find it is hard to reproduce sound that high up. When you consider aural masking, it is clear it could only be audible against a quiet background and with the equal loudness curves, only at a very high SPL.
Heck even if you can produce it and measure it, at 10MHz a strong airborne sound wave only travels a few inches before being fully absorbed, one guy selling magic super duper tweeters here was talking GHz frequencies (no kidding).
I agree with the frequency response observation and in fact most folks don’t realize that what one measures at the normal one meter, may be very different than what one would measure either indoors or out (no room effects) at the listening distance.
Just like with 99% of concert sound systems, the sound spectrum changes with distance and position if it isn’t constant directivity and even getting 20KHz to the listening position isn’t that easy..
I do agree, especially with your statement that "THIS is not the same as hearing / detecting a tone at those frequencies though and what people describe as "air" is more likely to be in the 8-10KHz range." The most striking demo I heard of a so-called super tweeter was in a situation where the main tweeter had no LP filter added and the "super" tweeter had a relatively low HP filter. The addition of the "super" tweeter was obvious but, because I know my own HF sensitivity roll-off, was probably due to intermodulation and increased output well down in the (commonly) audible range.
...think the exact same thing. Before I got into speaker design (including measurement) I thought the "sparkle and shimmer" was higher up too. It has components way high up I imagine, but you're right - it lives a lot lower down that many thing...
I'm not up on super tweeter theory by any means but I was under the impression that their Raison d'être was more for treble "ambiance" than actual frequency response extension. Kind of like adding subs to speakers that already offer good bass.
Indeed, to go along with your frequency response arguments most men over the age of 40 can't hear above 15khz let alone worrying about 20 or 22.5khz.
I suspect it has less to do with the frequency response and perhaps how they affect other frequencies lower down into the audible spectrum. Then again it could be BS to sell you something that does nothing in the real world. Until I've heard them in some kind of numbers I'll reserve judgement.
Post a Followup:
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: